patch 8.1.0570: 'commentstring' not used when adding fold marker

Problem:    'commentstring' not used when adding fold marker. (Maxim Kim)
Solution:   Only use empty 'comments' middle when leader is empty. (Christian
            Brabandt, closes #3670)
diff --git a/src/version.c b/src/version.c
index 312eca2..8df3ac7 100644
--- a/src/version.c
+++ b/src/version.c
@@ -793,6 +793,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    570,
+/**/
     569,
 /**/
     568,